1. Field of the Invention
The present invention relates to a cathode ray tube (CRT) apparatus used for a projection TV system (projector), more particularly to a CRT apparatus for a projection TV system which improves the purity of color of the light emitted therefrom.
2. Description of the Related Art
Television systems which have larger display screens and which are able to display larger images as compared with ordinary TV systems, include front type and rear projection type TV systems. In such projection TV systems, separate images are emitted from red (R), green (G), and blue (B) projection CRTs and are focused on a display screen to produce a single color image. Projection lenses are disposed at the front of the projection cathode ray tubes. On the inside surface of a panel glass of each CRT, a phosphor coating corresponding to each color is formed, and light is emitted in a predetermined pattern by irradiation of electron beams from an electron gun. The respective panel glasses emit the different colors of image light.
In such a projection TV system, since luminance is determined prior to the determination of the material of the phosphor, the distribution of the spectrum of the luminescence of the phosphor is generally broad and the color purity is insufficient. Further, since the spectrum of the luminescence is broad, chromatic aberration will occur due to the projection lens and thus image loss such as degradation of resolution, contrast, etc. will occur. In particular, there have been strong demands for improvement in the color purity in the CRT which produces green image light, which has a high luminosity factor.
Japanese Unexamined (Kokai) Patent Publication No. 3-61903 discloses a projection TV system in which the projection lenses have a light-absorbing substance added which absorbs light of the side bands of the luminescent characteristics of the cathode ray tubes. In the projection type TV system, it is possible to prevent image degradation to a certain extent. However, projection lenses especially for each color of R, G, and B are necessary and these have to be separately attached to the front of the cathode ray tubes. This makes the manufacturing process complicated and results in an increase in the manufacturing costs.